Japanese Examined Patent Application Publication No. 02-53805 describes a position detecting device in which a reflective signal is transmitted by a position pointer in sync with a signal transmitted from a tablet where a loop coil is provided. The reflective signal is received by the loop coil in the tablet to detect a position.
Additionally, Japanese Published Patent Application No. 10-214148 describes a position detecting device in which a power supply unit is incorporated in a position pointer. In this case, signal transmission is performed using a power supply, which increases transmission power, enabling accuracy of the position detection operation to be improved. Transmission of other identification information and like may also be performed. In other words, a power supply is typically included in position pointers that transmit a signal to the loop coil in the tablet to detect a position.
For example, it is known to use an input device to input position information to a computer. The input device detects a position designated on a board called a “tablet/digitizer” and inputs the position information to the computer. In the tablet/digitizer, a position detecting device is used to detect the designated position. Here, various technologies have been developed for detecting the position designated on the board. For example, a position detecting device that uses an electromagnetic induction method has been determined to be efficient, because of a high degree of reliability and other advantages based on non-contact detection.
When the electromagnetic induction position detecting device is used, an alternating magnetic-field signal is transmitted from a loop coil provided in a tablet. The alternating magnetic-field signal is then tuned and received by a resonant circuit provided in a position pointer. In response, a resonant signal generated in the resonant circuit of the position pointer is transmitted from a coil of the resonant circuit of the position pointer back to the tablet. The resonant signal is then received by the same or a different loop coil in the tablet. A position designated by the position pointer is then detected from a waveform of the received signal. Therefore, the position designated can be detected while the tablet and the position pointer are not in contact with each other.
The electromagnetic induction position detecting device may alternatively include a position pointer having a power supply unit incorporated therein, and an oscillating circuit provided to increase transmitting power, thereby improving the reliability of position detection. Additionally, when a plurality of pointers are used, identification information can be transmitted to the tablet along with position information.